The present disclosure relates to a drive transmission mechanism that transmits a driving force to a rotated member incorporated in an image forming apparatus such as a digital copier or a laser printer, and to an image forming apparatus incorporating such a drive transmission mechanism.
Commonly, in conventional drive transmission mechanisms used in driving portions in image forming apparatuses exploiting electrophotography, such as copiers, printers, and facsimile machines, rotary members such as photosensitive drums and developing rollers are typically used as driven members. To transmit a rotation driving force to such rotary members, there is known a drive transmission mechanism composed of a drive transmission gear for transmitting the rotation driving force of a driving portion, and a coupling (shaft coupling) coupling a rotary member (driven member)-side rotary shaft with a driving portion-side rotary shaft.
When a driving force is transmitted to a driven member by use of a driving portion composed of such a drive transmission gear and a coupling, axis misalignment may occur between their axes of rotation. Commonly, in one conventional configuration, both the drive transmission gear and the coupling are inclined with respect to the axis of rotation to perform axis alignment, or the coupling alone is inclined with respect to the drive transmission gear to perform axis alignment.
However, when a driving force is transmitted to a driven member such as a photosensitive drum which requires rotation with high accuracy, the driving portion needs to be rigid. In that case, with conventional axis alignment as described above, the drive transmission mechanism has reduced rigidity. More particularly, when a resin gear having comparatively low rigidity is used as a drive transmission gear, a gear surface (rim) is more likely to incline (slant) due to deformation of a web surface. Also, when the drive transmission gear is a helical gear, a load is applied in the thrust direction of the gear, and thus as the load varies, the amount of deformation varies, and the rotation of the gear varies accordingly.
As a method for suppressing axis misalignment between axes of rotation in a drive transmission mechanism, for example, there is known an image forming apparatus incorporating a drive transmission mechanism using an Oldham coupling that absorbs eccentricity and axis angle misalignment during rotation.
There is also known an image forming apparatus in which a driven-side (developer carrying member-side) rotation engaging portion is fitted to a driving-side rotation engaging portion such that fine alignment is performed with the driven-side rotation engaging portion fixed. In this image forming apparatus, a rotation driving force used for surface movement of a developer carrying member is transmitted, and a shaft arranged in at least one end part of a transmission gear that meshes with the driven-side rotation engaging portion is engaged with an image forming apparatus main body-side positioning portion, thereby to achieve positioning of a developer carrying member inside the main body of the image forming apparatus.